The present invention pertains in general to data converters and, more particularly, to a time domain data converter with the output thereof processed through a frequency domain transform to provide an output in the frequency domain.
Conventional data converters provide either conversion from the analog domain to the digital domain in a typical analog-to-digital converter, or from the digital domain to an analog domain as a digital-to-analog converter. Typical analog-to-digital (A/D) converters of the delta sigma type provide some type of analog modulator for providing the initial data conversion, which is then followed by some type of filtering step. Conventionally, the filtering is performed in part in the digital domain. This requires some type of digital processing of the digital output of the modulator in the form of a digital filter such as a Finite Impulse Response (FIR) filter. However, the digital values output therefrom are values that exist in the time domain.
In some applications, it is desirable to determine information in the frequency domain after the conversion operation. Such applications as spectrum analyzers, for example, require such information. Therefore, the output of the data converter in the digital domain is then processed through some type of transform for converting time domain information to frequency domain information, this all completed in the digital domain.
The types of transform engines that are utilized to convert time domain information to digital domain information typically utilize some type of Fourier Transform, the most common being a Discrete Fourier Transform (DFT). The DFT is a one-to-one mapping of any finite sequence {y(r)}, r=0, 1, 2 . . . , Nxe2x88x92 1 of N samples onto another sequence. This is defined by the following relationship:       Y    ⁡          (      k      )        =            ∑              r        =        0                    N        -        1              ⁢          xe2x80x83        ⁢                  y        ⁡                  (          r          )                    ⁢              w        N        rk            
where:             w      N        ≡          ⅇ                        -          j                ⁢                  xe2x80x83                ⁢        2        ⁢                  π          /          N                      =            cos      ⁢                        2          ⁢          π                N              -          j      ⁢              xe2x80x83            ⁢      sin      ⁢                        2          ⁢          π                N            
In general, a DFT algorithm requires a plurality of multiplication/accumulation operations. To reduce the number of these multiplication/accumulations, a Fast Fourier Transform (FFT) can be implemented to provide a rapid means for computing a DFT with Nlog2N multiplies, which otherwise would have taken N2 complex multiplications. Even with the reduction of the number of multiplications, there are still a large number of multiplication/accumulation operations that are required in order to calculate the time domain/frequency domain conversion. Conventionally, a Digital Signal Processor (DSP) is required which is typically a separate integrated circuit. As such, whenever providing for both a data conversion operation with an A/D converter, and a time domain/frequency domain conversion with a DSP, there are typically required two integrated circuits.
In general, there does not exist a commercial monolithic solution providing both the benefits of a data converter with that of a frequency domain converter such that an analog input can be received, converted to the digital domain and this digital value processed to provide a frequency domain output. In general, typical solutions utilize a data converter that provides a digital value in the time domain which is then input to a processor. This processor can be in the form of a microcontroller or a DSP. A data converter, due to its inherent construction, basically provides the ability to convert an analog input signal to a digital time domain output signal with a defined bit-resolution. This, of course, provides an output in the time domain. When processing this time domain signal to provide a frequency domain output, the processor is programmed to process some type of Discrete Fourier Transform or Fast Fourier Transform. Any type of algorithm that provides such a transform can be utilized. However, in order for a designer to utilize such a transform, this requires programming of the processor or microcontroller. Therefore, if an existing design must be upgraded to provide such a function or be required to process in the frequency domain, then a more complex DSP or microcontroller must be utilized. This is due to the fact that any processing in the frequency domain requires a more complex processing capability. The result is that an upgrade to a frequency domain solution from a time domain solution will probably require the designer to change his design to incorporate a much more complex processing section, in addition to also requiring a significant amount of programming of that processing section, this programming being the most expensive aspect of such an upgrade. It is desirable to utilize the pre-upgrade processing section, which is typically a relatively simple processor, and merely upgrade the data converter. However, the mere change of a design to process in the frequency domain as opposed to the time domain will necessitate additional processing capability and programming.
The present invention disclosed and claimed herein comprises a data conversion circuit for converting data from an analog input value to a digital value. The data converter includes a time domain processor for receiving the analog input value and generating a digital value representative thereof in the time domain. A frequency domain processor is provided for receiving the output of the time domain processor and processing the time domain information therefrom through a predetermined time domain/frequency domain algorithm to output frequency domain information representative of the output of the time domain processor in the frequency domain in accordance with the algorithm. An input/output interface is operable to interface the output of at least the frequency domain processor for external access thereto. A controller generates data-ready signal when data is generated by the frequency domain processor to indicate to a user that data can be retrieved from the input/output interface.
In another aspect of the present invention, the data converter includes a time domain data converter for receiving the analog input, and converting the received analog input to a digital value, for a given sampled value of the received analog input value. A time domain input/output interface is provided for interfacing the output of the time domain converter for external access thereto. A background frequency domain processor is provided for receiving a plurality of successive outputs of the time domain data converter for processing with a predetermined time domain/frequency domain algorithm to provide frequency domain information relating to the successive outputs of the time domain data converter processed.